According to the protocol architecture described in 3GPP TS 24.007[20], each CM entity will have its own MM connection. These differentMM connections are identified by the protocol discriminator PD and,additionally, by the transaction identifier TI.

So for example, one could have multiple calls (same pdisc, but different TI),or one could have SMS ongoing while a call (different pdisc+TI).

Testing an SMS sent during an ongoing call indeed shows a secondary CM Service Request.

In attached pcap it seems that we are already handling the situation rather well.Nevertheless, take a close look:

are we handling the TI properly?

make sure that the tear down of one service handling doesn't cut short any other pending CM Service Requests, especially if one CM Service Request concludes while the another has just sent the CM Service Request and we are still waiting for the actual CC/RR/... service request following.

(I also notice in attached PCAP that DTMF requests are rejected, and that a call Hold command is rejected; that may have to become separate issues.)